U.S. patent application number 10/051285 was filed with the patent office on 2003-07-24 for system and method for treating skin.
This patent application is currently assigned to SYNERON MEDICAL LTD.. Invention is credited to Kreindel, Michael.
Application Number | 20030139740 10/051285 |
Document ID | / |
Family ID | 21970360 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030139740 |
Kind Code |
A1 |
Kreindel, Michael |
July 24, 2003 |
System and method for treating skin
Abstract
System and method for treating a skin target. A temperature
effector creates a temperature difference between the target and
the skin tissue surrounding the target such that the target is at a
higher temperature than the surrounding the. One or more RP
electrodes are attached to the skin and RE energy is applied.
Inventors: |
Kreindel, Michael; (Haifa,
IL) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.
624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Assignee: |
SYNERON MEDICAL LTD.
18 Copelevitch Street
OrAkiva
IL
|
Family ID: |
21970360 |
Appl. No.: |
10/051285 |
Filed: |
January 22, 2002 |
Current U.S.
Class: |
606/41 |
Current CPC
Class: |
A61B 2018/00452
20130101; A61B 18/14 20130101; A61B 2018/00023 20130101 |
Class at
Publication: |
606/41 |
International
Class: |
A61B 018/18 |
Claims
1. A system for treating a skin target comprising: (a) one or more
RF electrodes configured to be attached to the skin, so as to apply
an RF current to the skin; (b) a temperature effector configured to
create a temperature difference between the target and skin
surrounding the target such that the target is at a higher
temperature than the surrounding tissue.
2. The system according to claim 1 wherein the temperature effector
heats the target.
3. The system according to claim 2 wherein the temperature effector
comprises a light source configured to apply optical energy to the
target.
4. The system according to claim 1 wherein the temperature effector
cools the surrounding tissue.
5. The system according to claim 4 wherein the temperature effector
comprises an irrigation unit cooling a fluid and tubes for allowing
the cooled fluid to flow near the surrounding skin.
6. A method for treating a skin target comprising: (a) creating a
temperature gradient between the target and skin surrounding the
target such that the target is at a higher temperature than the
surrounding skin; and (b) applying RF energy to the skin.
7. The method according to claim 6 wherein the temperature gradient
is created by heating the target.
8. The method according to claim 7 wherein the target is heated by
applying optical energy to the target.
9. The method according to claim 5 wherein the temperature gradient
is created by cooling the skin surrounding the target.
10. The met-hod according to claim 9 wherein the surrounding skin
is cooled by contacting the skin with a pre-cooled fluid.
11. The method according to claim 6 wherein the target is selected
from the group comprising a vascular lesion, pigmented lesion, hair
follicle, wrinkle and acne.
Description
FIELD OF THE INVENTION
[0001] This invention relates to methods and systems for treating
skin.
BACKGROUND OF THE INVENTION
[0002] The term "target" is used herein to denote a skin defect
such as a vascular lesion, pigmented lesion, acne, unwanted hair or
wrinkle. Selective thermal treatment of skin is commonly used in
aesthetic medicine to remove skin targets. In order to be
destroyed, the target must be raised to a temperature of about
70.degree. C. without raising the temperature of the surrounding
epidermis or dermis to damaging levels. The most popular method of
thermal skin treatment is selective photo-thermolysis in which
light energy produced by a laser or flash lamp is selectively
absorbed by a pigmented portion of the target. However, with this
method it is often not possible to heat the entire target to a
temperature necessary for destroying it without heating the
surrounding skin to damaging levels. The main problem is that the
optical contrast between the target and the surrounding skin tissue
is not high enough to obtain a significant difference in
temperature between the target and the surrounding skin tissue.
[0003] U.S. Pat. No. 5,755,753 disclose use of the radio-frequency
(RF) range of electro-magnetic energy for skin tightening, where RF
energy is applied to a pre-cooled skin surface. U.S. Pat. No.
5,846,252 discloses treating hairs to reduce their electrical
resistance and then applying RF current.
SUMMARY OF THE INVENTION
[0004] The present invention is based upon the finding that
selective heating of a skin target by RF energy is enhanced if
prior to the application of the RF energy the skin is treated to
make the temperature of the target (T.sub.t) higher than the
temperature of the surrounding skin tissue (T.sub.s). The initial
temperature gradient (T.sub.t-T.sub.s>0) between tie target and
surrounding tissue may be achieved either by preheating the target
or pre-cooling the surrounding tissue.
[0005] The invention thus provides a system for treating a skin
target comprising:
[0006] (a) one or more RF electrodes configured to be attached to
the skin, so as to apply an RF current to the skin;
[0007] (b) a temperature effector configured to create a
temperature gradient between the target and skin surrounding the
target such that the target is at a higher temperature than the
surrounding skin.
[0008] The invention still further provides a method for treating a
skin target comprising:
[0009] a) creating a temperature gradient between the target and
skin surrounding the target such that he target is at a higher
temperature than the surrounding skin; and
[0010] b) applying RF energy to the skin.
[0011] The system and method of the invention may be used for such
skin targets as a vascular lesion, pigmented lesion, hair follicle,
wrinkle and acne.
[0012] While not wishing to be bound by a particular theory, it is
believed that selective thermolysis of a target by RF energy is
enhanced when T.sub.t-T.sub.s>0 due to an increase in the
electrical conductivity in the RF range of tissues when thee tissue
temperature is increased [Frances A. Duck, Physical Properties of
Tissue, a Comprehensive Reference Book, Academic Press, 1990,
p.173]. Accordingly, the dependence of the conductivity a of a
tissue on temperature T is given by:
.sigma.=.sigma..sub.0(1+.alpha.(T-T.sub.0)) (1)
[0013] where .sigma..sub.0 is the conductivity at the reference
temperature T.sub.0 and .alpha. is a constant known as the
temperature coefficient.
[0014] Heat generation by RF current can be estimated by Joule's
Law:
H=.sigma.E.sup.2 (2)
[0015] and the change in temperature in the tissue is obtained
using the heat conductivity equation: 1 c T t = H ( 3 )
[0016] where c is the heat capacity of the tissue, .rho. is the
mass density and E is the intensity of the electric field.
[0017] Inserting Equations 1 and 2 into (3), 2 c T t = o ( 1 + ( T
- T o ) E 2 ( 4 ) Setting A = o E 2 c ( 5 )
[0018] and integrating Equation 4, the result is 3 T ' = T o + At -
1 + ( T i - T o ) At ( 6 )
[0019] where T.sub.i is the initial temperature of the tissue
before the application of RF energy, t is the duration of the
application of RF energy, and T' is the formal temperate of tie
tissue at the end of the application of RF energy.
[0020] If the initial temperatures of the target and sounding skin
tissue are T.sub.t and T.sub.s respectively (T.sub.tT.sub.s>0),
then Equation 6 becomes for the target: 4 T t ' = T o + At - 1 + (
T ij - T to ) A it ( 7 )
[0021] and for the surrounding skin, 5 T s ' = T 0 ' + At - 1 + ( T
st - T o ) At ( 8 )
[0022] subtracting Equation (8) from Equation (7) yields
T'.sub.t-T'.sub.s=(T.sub.ti-T.sub.si)e.sup.At (9)
[0023] where T.sub.ti-T.sub.si is the initial temperate gradient
between the target and the surrounding skin, and T'.sub.t-T'.sub.s
is the final temperature gradient. Equation (9) shows that as the
RF current is applied, the temperature gradient increases
exponentially. Therefore, by creating an initial relatively small
temperature gradient T.sub.ti-T.sub.si>0, and applying RF
energy, a larger temperature gradient is obtained. This allows
heating of the target to a sufficiently high temperature to destroy
the target without heating the surrounding skin tissues to damaging
levels.
[0024] Assuming a typical RF fluence (F) in the skin of 20
J/cm.sup.2, .alpha.=0.03 (C.degree.).sup.-1 and a heat capacitance
c.rho.=3.6 J/cm.sup.3.degree.K the factor e.sup.At in Equation (9)
is 6 At = e o E 2 c = e Ht c = 0.83 = 2.3
[0025] Thus, the temperature gradient increases by a factor of
about 2.3 during the application of the RF energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In order to understand the invention and to see how it may
be carried out in practice, a preferred embodiment will now be
described, by way of non-limiting example only, with reference to
the accompanying drawings, in which:
[0027] FIG. 1 shows a system for heating a skin target and applying
RF to an individual in accordance with one embodiment of the
invention;
[0028] FIG. 2 shows a method for treating skin using the system of
FIG. 1;
[0029] FIG. 3 shows an applicator with two electrodes, and a light
source used in tie system of FIG. 1.
[0030] FIG. 4 shows a system for cooling skin surrounding a target
and applying RF energy to an individual in accordance with another
embodiment of the invention;
[0031] FIG. 5 shows an applicator with two electrodes, and a
cooling system used in the system of FIG. 3; and
[0032] FIG. 6 shows a method for treating skin using the system of
FIGS. 4 and 5.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Referring to FIGS. 1 and 2, a system for creating a temper
gradient between a skin target and the surrounding skin, in
accordance with the invention is shown. An applicator 703, to be
described in detail below, contains a pair of RF electrodes 401 and
402 and a light source 403. The applicator 703 is adapted to be
applied to the skin of an individual 705 in the region of a target.
The applicator 703 is connected to a control unit 701 via a cable
702. The control unit 701 includes a power source 708. The power
source 708 is connected to an RF generator 715 that is connected to
the RF electrodes in the applicator 703 via wires in the cable 702.
The power source 708 is also connected to a light source 403 in the
applicator 703 via wires in the cable 702. The control unit 701 has
an input device such as a keypad 710 that allows an operator to
input selected values of parameters of the treatment, such as the
frequency, pulse duration and intensity of the RF energy or the
wavelength and intensity of the optical energy. The control unit
701 optionally contains a processor 709 for monitoring and
controlling various functions of the device. For example, the
processor 709 may monitor the electrical impedance between the
electrodes in the applicator 703, and determine the temperature
distribution in the vicinity of the target. The processor 709 may
also determine the parameters of the treatment based upon the
impedance measurements.
[0034] FIG. 2 shows the applicator 703 in detail. The applicator
contains a pair of electrodes 401 and 402 that apply RF energy to
the skin. A light source 403 produces a light spectrum that is
delivered to the skin surface by light guide 404.
[0035] In accordance with the method of the invention, the system
shown in FIG. 1 is used to first apply optical energy to a target
having a diameter for example of 2 mm. The optical energy may have
an intensity from about 5 to about 100 Joules/cm.sup.2 and may be
applied from about 1 to 200 msec.
[0036] The parameters of RF energy may have the following exemplary
values:
[0037] Frequency of the RF energy: from about 300 kHz to about 100
MHz.
[0038] Output power of the RF energy from about 5 to about 200
W.
[0039] Duration of the irradiation: from about 1 to about 500
msec.
[0040] Pulse repetition rate: from about 0.1 to about 10 pulses per
second.
[0041] FIG. 3 shows a flow chart for a method of treating skin
using the system shown in FIGS. 1 and 2. In step 300, the
applicator 703 is applied to the skin of an individual in the
region of a target in the skin. In step 310 the light source 403 is
activated so that the target is irradiated with optical energy from
the light source 403 conducted through the optic fiber 404 to the
target. In step 320 the irradiation with optical energy is
terminated. RF energy is then applied to the skin (step 330).
Finally, in step 340, the application of RF energy is
terminated.
[0042] Referring now to FIGS. 4 and 5, a system for creating a
temperature gradient between a skin target and the surrounding ski,
in accordance with another embodiment of the invention is shown. An
applicator 803, to be described in detail below, contains a pair of
RF electrodes 401 and 402. The applicator 803 is adapted to be
applied to the skin of an individual 805 in the region of a target.
The control unit 801 includes a power source 808. The power source
808 is connected to an RF generator 815 that is connected to the RF
electrodes in the applicator 803 via wires in the cable 802. The
control unit 801 controls a refrigeration unit 812 that cools a
fluid such as ethanol or water for cooling the applicator 803. The
cooled fluid flows 10 from the refrigeration unit 812 to the
applicator via a first tube in the cable 802, and flows from the
applicator 803 back to the refrigeration unit via a second tube in
the cable 802. The control unit 801 has an input dice such as a
keypad 810 that allows an operator to input selected values of
parameters of the treatment, such as the frequency, pulse duration
and intensity of the RF energy or the temperature of the coating
fluid. The control unit 801 optionally contains a processor 809 for
monitoring and controlling various functions of the device. For
example, the processor 809 may monitor the electrical impedance
between the electrodes in the applicator 803, and determine the
temperature distribution in the vicinity of the target. The
processor 809 may also determine the parameters of the treatment
based upon the impedance measurements.
[0043] FIG. 5 shows the applicator 803 in, detail. The applicator
contain a pair of electrodes 401 and 402 that apply RF energy to
the skin. The housing and electrodes are cooled by fluid cooled by
the refrigeration unit 812 that flows in a tube 408 between inlet
405 and outlet 406. The inlet 405 and the outlet 406 are connected
to the refrigeration unit 812 via the fist and second tubes in the
cable 802.
[0044] FIG. 6 shows a flow chart for a method of treating skin
using the system shown in FIGS. 4 and 5. In step 600, the
applicator 703 is applied to the skin of an individual in the
region of a target in the skin. In step 610 cooling system 812 is
activated so that the skin surrounding the target is cooled to a
temperature below that of the target, RF energy is then applied to
the skin (step 620). Finally, in step 630, the application of RF
energy is terminated.
* * * * *